Recombinant DNA technology has been applied in the isolation of natural genes and the expression of these genes in a variety of host cells. Typically, this technology has had utility in producing biologically active polypeptides, such as interferons or peptide hormones, which were impractical to produce in useful amounts by other means. It was also possible to produce modified proteins by isolating natural genes and utilizing the techniques of site specific, in vitro mutagenesis to alter these genes and thereby change the polypeptides produced. Other polypeptides have been created by combining sections of various native genes to produce new polypeptides that are chimeric molecules of the several naturally occurring molecules.
With the advent of efficient and automated methods for the chemical synthesis of DNA, it has become possible to synthesize entire genes and to modify such synthetic genes at will during the course of synthesis. However, these various technologies have been applied to the production of natural or modified versions of natural polypeptides. There have been very few attempts to use these technologies to create substantially new polypeptides. In nature, polypeptides have a wide range of chemical, physical and physiological characteristics. Nevertheless, there are commercial applications for which known, naturally occurring polypeptides are not appropriate.
While biotechnology is versatile, usually it has been limited in its applications to naturally occurring products or modifications of naturally occurring molecules. One great strength of organic chemical synthesis, by contrast, has been the ability to transform inexpensive carbon materials to a wide variety of polymeric molecules, including naturally occurring molecules, but most importantly entirely new chemical structures, such as polypropylene and polyacrylates, which have defined and predicted chemical properties not associated with naturally occurring molecules.
Such materials, particularly high-molecular-weight polymers containing repeating sequences of amino acids, have proven difficult to produce by biochemical means. The genes necessary for producing large peptides containing repeating units of amino acids were unstable and often underwent intermolecular recombination causing deletions of repeating units in the gene. The development of a biotechnology which would produce polymeric molecules by biological processes similar to those available by organic synthesis would significantly broaden the range of applications of biotechnology.